diff --git a/conservancy_beancount/plugin/meta_invoice.py b/conservancy_beancount/plugin/meta_invoice.py
new file mode 100644
index 0000000000000000000000000000000000000000..47866abbf08b17e42e87f358cfa0db39f946b637
--- /dev/null
+++ b/conservancy_beancount/plugin/meta_invoice.py
@@ -0,0 +1,40 @@
+"""meta_invoice - Validate invoice metadata"""
+# Copyright © 2020  Brett Smith
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+from . import core
+from .. import data
+from .. import errors as errormod
+from ..beancount_types import (
+    MetaValueEnum,
+    Transaction,
+)
+
+class MetaInvoice(core._PostingHook):
+    METADATA_KEY = 'invoice'
+    HOOK_GROUPS = frozenset(['metadata', METADATA_KEY])
+
+    def _run_on_post(self, txn: Transaction, post: data.Posting) -> bool:
+        return post.account.is_under('Accrued') is not None
+
+    def post_run(self, txn: Transaction, post: data.Posting) -> errormod.Iter:
+        try:
+            problem = not post.meta.get_links(self.METADATA_KEY)
+            value = None
+        except TypeError:
+            problem = True
+            value = post.meta[self.METADATA_KEY]
+        if problem:
+            yield errormod.InvalidMetadataError(txn, self.METADATA_KEY, value, post)
diff --git a/tests/test_meta_invoice.py b/tests/test_meta_invoice.py
new file mode 100644
index 0000000000000000000000000000000000000000..5586e75b4f78d521fb2d715ab5fdb2300664a75c
--- /dev/null
+++ b/tests/test_meta_invoice.py
@@ -0,0 +1,139 @@
+"""Test validation of invoice metadata"""
+# Copyright © 2020  Brett Smith
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+import pytest
+
+from . import testutil
+
+from conservancy_beancount.plugin import meta_invoice
+
+VALID_VALUES = {
+    'Invoices/304321.pdf',
+    'rt:123/456',
+    'rt://ticket/234',
+}
+
+INVALID_VALUES = {
+    '',
+    ' ',
+    '     ',
+}
+
+REQUIRED_ACCOUNTS = {
+    'Accrued:AccountsPayable',
+    'Accrued:AccountsReceivable',
+}
+
+NON_REQUIRED_ACCOUNTS = {
+    'Assets:Cash',
+    'Expenses:Other',
+    'Income:Other',
+    'Liabilities:CreditCard',
+    'UnearnedIncome:Donations',
+}
+
+TEST_KEY = 'invoice'
+
+@pytest.fixture(scope='module')
+def hook():
+    config = testutil.TestConfig()
+    return meta_invoice.MetaInvoice(config)
+
+@pytest.mark.parametrize('acct1,acct2,value', testutil.combine_values(
+    REQUIRED_ACCOUNTS,
+    NON_REQUIRED_ACCOUNTS,
+    VALID_VALUES,
+))
+def test_valid_values_on_postings(hook, acct1, acct2, value):
+    txn = testutil.Transaction(postings=[
+        (acct2, -25),
+        (acct1, 25, {TEST_KEY: value}),
+    ])
+    assert not list(hook.run(txn))
+
+@pytest.mark.parametrize('acct1,acct2,value', testutil.combine_values(
+    REQUIRED_ACCOUNTS,
+    NON_REQUIRED_ACCOUNTS,
+    INVALID_VALUES,
+))
+def test_invalid_values_on_postings(hook, acct1, acct2, value):
+    txn = testutil.Transaction(postings=[
+        (acct2, -25),
+        (acct1, 25, {TEST_KEY: value}),
+    ])
+    actual = {error.message for error in hook.run(txn)}
+    assert actual == {"{} missing {}".format(acct1, TEST_KEY)}
+
+@pytest.mark.parametrize('acct1,acct2,value', testutil.combine_values(
+    REQUIRED_ACCOUNTS,
+    NON_REQUIRED_ACCOUNTS,
+    testutil.NON_STRING_METADATA_VALUES,
+))
+def test_bad_type_values_on_postings(hook, acct1, acct2, value):
+    txn = testutil.Transaction(postings=[
+        (acct2, -25),
+        (acct1, 25, {TEST_KEY: value}),
+    ])
+    expected_msg = "{} has wrong type of {}: expected str but is a {}".format(
+        acct1,
+        TEST_KEY,
+        type(value).__name__,
+    )
+    actual = {error.message for error in hook.run(txn)}
+    assert actual == {expected_msg}
+
+@pytest.mark.parametrize('acct1,acct2,value', testutil.combine_values(
+    REQUIRED_ACCOUNTS,
+    NON_REQUIRED_ACCOUNTS,
+    VALID_VALUES,
+))
+def test_valid_values_on_transaction(hook, acct1, acct2, value):
+    txn = testutil.Transaction(**{TEST_KEY: value}, postings=[
+        (acct2, -25),
+        (acct1, 25),
+    ])
+    assert not list(hook.run(txn))
+
+@pytest.mark.parametrize('acct1,acct2,value', testutil.combine_values(
+    REQUIRED_ACCOUNTS,
+    NON_REQUIRED_ACCOUNTS,
+    INVALID_VALUES,
+))
+def test_invalid_values_on_transaction(hook, acct1, acct2, value):
+    txn = testutil.Transaction(**{TEST_KEY: value}, postings=[
+        (acct2, -25),
+        (acct1, 25),
+    ])
+    actual = {error.message for error in hook.run(txn)}
+    assert actual == {"{} missing {}".format(acct1, TEST_KEY)}
+
+@pytest.mark.parametrize('acct1,acct2,value', testutil.combine_values(
+    REQUIRED_ACCOUNTS,
+    NON_REQUIRED_ACCOUNTS,
+    testutil.NON_STRING_METADATA_VALUES,
+))
+def test_bad_type_values_on_transaction(hook, acct1, acct2, value):
+    txn = testutil.Transaction(**{TEST_KEY: value}, postings=[
+        (acct2, -25),
+        (acct1, 25),
+    ])
+    expected_msg = "{} has wrong type of {}: expected str but is a {}".format(
+        acct1,
+        TEST_KEY,
+        type(value).__name__,
+    )
+    actual = {error.message for error in hook.run(txn)}
+    assert actual == {expected_msg}
diff --git a/tests/testutil.py b/tests/testutil.py
index 648e5ec17845e471509970105d8d81902f30cc5f..8dd7e1b8687d07cffc866d428d2a13e94ccb7830 100644
--- a/tests/testutil.py
+++ b/tests/testutil.py
@@ -43,6 +43,12 @@ def check_post_meta(txn, *expected_meta, default=None):
             }
             assert actual == expected
 
+def combine_values(*value_seqs):
+    return itertools.islice(
+        zip(*(itertools.cycle(seq) for seq in value_seqs)),
+        max(len(seq) for seq in value_seqs),
+    )
+
 def parse_date(s, fmt='%Y-%m-%d'):
     return datetime.datetime.strptime(s, fmt).date()